U.S. patent application number 11/079519 was filed with the patent office on 2005-09-29 for distributed cooling system.
Invention is credited to Nash, Robert V. JR..
Application Number | 20050210901 11/079519 |
Document ID | / |
Family ID | 34994251 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050210901 |
Kind Code |
A1 |
Nash, Robert V. JR. |
September 29, 2005 |
Distributed cooling system
Abstract
A system includes a plurality of distributed refrigeration units
respectively coupled to discrete refrigeration circuits. Each
refrigeration unit may include a variable compressor, a fixed
compressor, a condensing unit, and a controller. The controller
compares an operating condition of the refrigeration unit to a
refrigeration circuit set point to select a compressor staging
capable of achieving the refrigeration circuit set point.
Inventors: |
Nash, Robert V. JR.; (Niles,
MI) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
34994251 |
Appl. No.: |
11/079519 |
Filed: |
March 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60553056 |
Mar 15, 2004 |
|
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|
Current U.S.
Class: |
62/228.5 ;
62/510 |
Current CPC
Class: |
Y02B 30/743 20130101;
F25B 2400/075 20130101; F25B 2600/111 20130101; Y02B 30/70
20130101; F25B 2700/1933 20130101; F25B 2600/0253 20130101; F25B
2400/22 20130101; Y02B 30/741 20130101; F25B 49/022 20130101 |
Class at
Publication: |
062/228.5 ;
062/510 |
International
Class: |
F25B 005/00; F25B
001/00; F25B 049/00; F25B 001/10 |
Claims
What is claimed is:
1. A system comprising: a first refrigeration unit including a
first variable capacity compressor operable between a full capacity
mode and a reduced capacity mode and a first fixed capacity
compressor operable between a full capacity mode and a zero
capacity mode, said first variable capacity compressor and said
first fixed capacity compressor being fluidly coupled to a first
suction manifold and fluidly coupled to a first discharge manifold,
said first suction manifold and said first discharge manifold
coupled to a first refrigeration circuit operating within a first
temperature range; a first controller associated with said first
refrigeration unit to stage said first variable capacity compressor
and said first fixed capacity compressor based on a comparison of a
first operating condition of said first refrigeration unit to a
first refrigeration circuit set point; a second refrigeration unit
including a second variable capacity compressor operable between a
full capacity mode and a reduced capacity mode and a second fixed
capacity compressor operable between a full capacity mode and a
zero capacity mode, said first variable capacity compressor and
said first fixed capacity compressor being fluidly coupled to a
second suction manifold and fluidly coupled to a second discharge
manifold, said second suction manifold and said second discharge
manifold coupled to a second refrigeration circuit separate from
said first refrigeration circuit and operating within a second
temperature range different than said first temperature range; and
a second controller associated with said second refrigeration unit
to stage said second variable capacity compressor and said second
fixed capacity compressor based on a comparison of a second
operating condition of said second refrigeration unit to a second
refrigeration circuit set point.
2. The system of claim 1, wherein said first operating condition is
a first suction pressure and said second operating condition is a
second suction pressure.
3. The system of claim 2, wherein said first suction pressure is
detected at said first suction manifold and said second suction
pressure is detected at said second suction manifold.
4. The system of claim 1, wherein said first controller uses
proportional integral control in comparing said first operating
condition to said first refrigeration circuit set point and said
second controller uses proportional integral control in comparing
said second operating to said second refrigeration circuit set
point.
5. The system of claim 1, wherein said first controller selects
compressor staging for said first refrigeration circuit using a
compressor control algorithm and said second controller selects
compressor staging for said second refrigeration circuit using a
compressor control algorithm.
6. The system of claim 1, wherein said first controller selects
compressor staging using a first look-up table and said second
controller selects compressor staging using a second look-up
table.
7. The system of claim 6, wherein said first and second look-up
tables each include all possible combinations of compressor
staging.
8. The system of claim 1, wherein said first controller modulates a
capacity of said first variable capacity compressor to achieve said
first refrigeration circuit set point and said second controller
modulates said second variable compressor to achieve said second
refrigeration circuit set point.
9. The system of claim 8, wherein said first controller selectively
toggles said first fixed compressor between a run state and a
shutdown state to achieve said first refrigeration circuit set
point and said second controller selectively toggles said second
fixed compressor between a run state and a shutdown state to
achieve said second refrigeration circuit set point.
10. The system of claim 1, wherein said first refrigeration unit
includes a first condensing unit having a first condenser coil and
a first condenser fan and said second refrigeration unit includes a
second condensing unit having a second condenser coil and a second
condenser fan.
11. The system of claim 10, wherein said first controller is
operable to control said first condenser fan based on said first
refrigeration circuit set point and said second controller is
operable to control said second condenser fan based on said second
refrigeration circuit set point.
12. The system of claim 1, wherein said first controller is in
communication with a system controller and said second controller
is in communication with a system controller.
13. For a refrigeration circuit in a refrigeration system including
multiple refrigeration circuits, a refrigeration unit comprising: a
housing; at least one variable compressor disposed within said
housing; at least one fixed compressor disposed within said
housing; a suction manifold disposed within said housing and
fluidly coupled to said at least one variable compressor and to
said at least one fixed compressor; a discharge manifold fluidly
disposed within said housing and coupled to said at least one
variable compressor and to said at least one fixed compressor; a
condenser unit disposed within said housing; and a controller
mounted to said housing and operable to stage said at least one
variable capacity compressor and said at least one fixed capacity
compressor based on a comparison of an operating condition to a set
point.
14. The refrigeration unit of claim 13, wherein said controller is
in communication with a system controller.
15. The refrigeration unit of claim 13, wherein said operating
condition is a suction pressure.
16. The refrigeration unit of claim 15, wherein said suction
pressure is detected at said suction manifold.
17. The refrigeration unit of claim 13, wherein said controller
uses proportional integral control in comparing said operating
condition to said set point.
18. The refrigeration unit of claim 13, wherein said controller
selects compressor staging using a compressor control
algorithm.
19. The refrigeration unit of claim 13, wherein said controller
selects compressor staging using a look-up table.
20. The refrigeration unit of claim 19, wherein said look-up table
includes all possible combinations of compressor staging.
21. The refrigeration unit of claim 13, further comprising a
condensing unit having a condenser coil and a condenser fan.
22. The system of claim 21, wherein said controller is operable to
control said condenser fan based on said first refrigeration
circuit set point.
23. A method comprising: selecting a first set point for a first
refrigeration circuit coupled to a first refrigeration unit having
a first variable capacity compressor and a first fixed capacity
compressor; detecting a first operating condition of said first
refrigeration circuit; comparing said first operating condition to
said first set point; staging said first variable capacity
compressor and said first fixed capacity compressor based on said
comparison; selecting a second set point for a second refrigeration
circuit coupled to a second refrigeration unit having a second
variable capacity compressor and a second fixed capacity
compressor; detecting a second operating condition of said second
refrigeration circuit; comparing said second operating condition to
said second set point; and staging said second variable capacity
compressor and said second fixed capacity compressor based on said
comparison.
24. The method of claim 23, wherein said detecting a first
operating condition includes detecting a combined suction pressure
of said first variable capacity compressor and said first fixed
capacity compressor and said detecting a second operating condition
includes detecting a combined suction pressure of said second
variable capacity compressor and said second fixed capacity
compressor.
25. The method of claim 23, wherein said comparing said first
operating condition to said first set point and said comparing said
second operating condition to said second set point includes using
proportional integral control.
26. The method of claim 23, wherein said wherein said staging said
first variable capacity compressor and said staging said second
variable capacity compressor includes use of a compressor control
algorithm.
27. The method of claim 23, wherein said staging said first
variable capacity compressor and said staging said second variable
capacity compressor includes referencing a capacity look-up
table.
28. The method of claim 27, wherein said referencing includes
selecting from all possible combinations of compressor staging.
29. The method of claim 23, further comprising modulating said
first variable capacity compressor to achieve said first set point
and modulating said second variable capacity compressor to achieve
said second set point.
30. The method of claim 29, further comprising selectively toggling
said first fixed capacity compressor between a run state and a
shutdown state to achieve said first set point and selectively
toggling said second fixed capacity compressor between a run state
and a shutdown state to achieve said second set point.
31. The method of claim 23, further comprising communicating
compressor staging information from said first refrigeration
circuit to a system controller and communicating compressor staging
information from said second refrigeration circuit to a system
controller.
32. A system comprising: a plurality of discrete refrigeration
units respectively coupled to independent refrigeration circuits,
each of said individual refrigeration circuits operating in a
different temperature range from another of said independent
refrigeration circuits; each of said discrete refrigeration units
including at least one compressor fluidly coupled to a suction
manifold and fluidly coupled to a discharge manifold; and each of
said plurality of discrete refrigeration units including a
controller to stage said at least one compressor based on a
comparison of an operating condition of a respective said
independent refrigeration circuit to a refrigeration circuit set
point.
33. The system of claim 32, wherein said operating condition is a
suction pressure.
34. The system of claim 33, wherein said suction pressure is
detected at said suction manifolds.
35. The system of claim 33, wherein said controller compares said
suction pressure to said refrigeration circuit set point to
determine a compressor capacity required to achieve said
refrigeration circuit set point.
36. The system of claim 35, wherein said controller uses
proportional integral control in comparing said suction pressure
and said refrigeration circuit set point.
37. The system of claim 35, wherein said controller selects said
compressor staging based on said required compressor capacity using
a compressor control algorithm.
38. The system of claim 35, wherein said controller selects said
compressor staging based on said required compressor capacity using
a look-up table.
39. The system of claim 38, wherein said look-up table includes all
possible combinations of compressor staging.
40. The system of claim 32, wherein each of said discrete
refrigeration units further includes a condensing unit having a
condenser coil and a condenser fan.
41. The system of claim 40, wherein said controller is operable to
control said condenser fan based on said refrigeration circuit set
point.
42. The system of claim 32, wherein said controller is in
communication with a system controller.
43. The system of claim 32, wherein each of said discrete
refrigeration units includes at least one fixed capacity
compressor.
44. The system of claim 32, wherein each of said discrete
refrigeration units includes at least one variable capacity
compressor.
45. The system of claim 32, wherein each of said discrete
refrigeration units includes at least one fixed capacity compressor
and at least one variable capacity compressor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/553,056, filed on Mar. 15, 2004. The disclosure
of the above application is incorporated herein by reference.
FIELD
[0002] The present teachings relate generally to cooling systems
and, more specifically, to cooling system architecture and
control.
BACKGROUND
[0003] Referring to FIG. 1, a block diagram of a conventional
refrigeration system 10 employing a central plant architecture,
which generally includes a plurality of compressors 12 piped
together in an equipment room 6 with a common suction manifold 14
and a discharge header 16 all positioned within a compressor rack
18. The compressor rack 18 compresses refrigerant vapor that is
delivered to an outdoor condenser 20 where the refrigerant vapor is
liquefied at high pressure. This high-pressure liquid refrigerant
is delivered to a plurality of refrigeration cases 22 in a floor
space 8 by way of piping 24.
[0004] Each refrigeration case 22 is arranged in separate circuits
26 consisting of a plurality of refrigeration cases 22 that operate
within a similar temperature range. FIG. 1 illustrates four (4)
circuits 26 labeled circuit A, circuit B, circuit C and circuit D.
Each circuit 26 is shown consisting of four (4) refrigeration cases
22. Those skilled in the art, however, will recognize that any
number of circuits 26 within a refrigeration system 10, as well as
any number of refrigeration cases 22 may be employed within a
circuit 26. As indicated, each circuit 26 will generally operate
within a certain temperature range. For example, circuit A may be
for frozen food, circuit B may be for dairy, circuit C may be for
meat, etc.
[0005] Because the temperature requirement is specific to each
circuit 26 but each of the circuits is supplied cooling capacity by
a central source, a pressure regulator 28 for each circuit 26 acts
to control the evaporator pressure and, hence, the temperature
range of the circuit, as dictated by the type of refrigeration
cases 22. Typically, each refrigeration case 22 includes an
evaporator and expansion valve (not shown), which may be either a
mechanical or an electronic valve for controlling the superheat of
the refrigerant and thus the temperature of the refrigeration
case.
[0006] The conventional central plant architecture for a cooling
system positions the compressor rack or multiple compressor racks
in designated space of a building, perhaps in the equipment room,
basement or a rooftop penthouse. In each scenario, the system
requires extensive suction and liquid piping throughout the
building to feed the refrigeration cases, coolers and/or air
conditioning systems. As best illustrated in FIG. 2, liquid and
suction piping for each compressor rack A-E must be piped to the
associated refrigerated cases 22 in its circuit (as indicated by
cross-hatching), often requiring piping to cross the entire
building and return. Further, the circuit includes a condenser,
which is typically positioned outside the building and requires
extensive piping to feed the refrigeration cases, coolers and/or
air conditioning systems.
[0007] Conventional central plant architecture requires an
extensive piping network with suction and liquid piping traversing
throughout the store to feed cases, coolers and air conditioning
units, which then all run back to a common point, i.e., a suction
header for one or more compressor racks. Because of the extensive
piping, conventional coding systems require an extensive amount of
refrigerant to simply fill the pipes. In addition to the cost of
additional refrigerant, the extensive piping network presents a
greater opportunity for refrigeration leaks and heat loss,
requiring sensors and insulation. Further, the cost and complexity
of field piping condensers is significant, as is the physical space
required for the central plant or the structural steel to
accommodate large central rooftop penthouses.
[0008] The communication and power supply network is also extensive
as a result of the central plant architecture. With reference to
FIG. 1, communication and control wiring for each refrigeration
case 22, pressure regulator 28, and sensors 36, 40 are supplied to
an analog input board 50 or are received from an input/output board
32 or a driver board 38 to optimize cooling system performance.
This extensive network of wires is expensive to design and install.
In fact, much of the wiring results from design limitations imposed
by the central plant architecture which places the main
refrigeration controller 30, input/output module 32, and ESR board
42 in a compressor room 6 and daisy chained via a communication bus
34 to facilitate the exchange of data between them.
[0009] For example, to control the various functions of the
refrigeration system 10, a main refrigeration controller 30
controls the operation of each pressure regulator 28, as well as
the suction pressure set point for the entire compressor rack 18.
The refrigeration controller 30 controls the bank of compressors 12
in the compressor rack 18 through the input/output board 32, which
includes relay switches to turn the compressors 12 on and off to
provide the desired suction pressure. A separate case controller
may be used to control the superheat of the refrigerant to each
refrigeration case 22 through an electronic expansion valve in each
refrigeration case 22 by way of a communication network or bus.
[0010] Further, in order to monitor the suction pressure for the
compressor rack 18, a pressure transducer 40 may be positioned at
the input of the compressor rack 18 or just past the pressure
regulators 28. The pressure transducer 40 delivers an analog signal
to an analog input board 38, which measures the analog signal and
delivers this information to the main refrigeration controller 30,
via the communication bus 34. Also, to vary the openings in each
pressure regulator 28, the driver board 38 drives up to eight (8)
pressure regulators 28. The driver board 38 includes eight (8)
drivers capable of driving the pressure regulators 28 via control
from the main refrigeration controller 30.
[0011] The central plant architecture is particularly inefficient
as a result of the compressor rack 18 supplying high-pressure
liquid refrigerant to multiple refrigeration circuits operating at
different temperatures. With reference again to FIG. 1, the suction
pressure at the compressor rack 18 is dependent on the temperature
requirement for each circuit 26. For example, assume circuit A
operates at 10.degree. F., circuit B operates at 15.degree. F.,
circuit C operates at 20.degree. F., and circuit D operates at
25.degree. F. The suction pressure at the compressor rack 18, which
is sensed through the pressure transducer 40, requires a suction
pressure set point based on the lowest temperature requirement for
all the circuits 26, which, for this example, is circuit A, or the
lead circuit. Therefore, the suction pressure at the compressor
rack 18 is set to achieve a 10.degree. F. operating temperature for
circuit A, which is able to operate most efficiently with a nearly
one hundred percent open pressure regulator 28. Because each
circuit 26 is operating at a different temperature, however, the
pressure regulators 28 in circuits B, C and D are closed a certain
percentage for each circuit 26 to control the corresponding
temperature for that particular circuit 26 and costing efficiency.
To raise the temperature to 15.degree. F. for circuit B, the
stepper regulator valve 28 in circuit B is closed slightly, the
valve 28 in circuit C is closed further, and the valve 28 in
circuit D is closed even further providing for the various required
temperatures. As a result, the central plant architecture dictates
certain inherent operative inefficiencies.
SUMMARY
[0012] A system includes a plurality of discrete refrigeration
units respectively coupled to independent refrigeration circuits,
with each of the individual refrigeration circuits operating in a
different temperature range from another of the independent
refrigeration circuits. Each of the discrete refrigeration units
includes at least one compressor fluidly coupled to a suction
manifold and fluidly coupled to a discharge manifold. Each of the
plurality of discrete refrigeration units includes a controller to
stage the at least one compressor based on a comparison of an
operating condition of a respective independent refrigeration
circuit to a refrigeration circuit set point.
[0013] A system includes a first refrigeration unit including a
first variable capacity compressor and a first fixed capacity
compressor fluidly coupled to a first suction manifold and fluidly
coupled to a first discharge manifold. The first suction manifold
and first discharge manifold are coupled to a first refrigeration
circuit operating within a first temperature range. A first
controller is associated with the first refrigeration unit to stage
the first variable capacity compressor and the first fixed capacity
compressor based on a comparison of a first operating condition of
the first refrigeration unit to a first refrigeration circuit set
point. A second refrigeration unit includes a second variable
capacity compressor and a second fixed capacity compressor fluidly
coupled to a second suction manifold and fluidly coupled to a
second discharge manifold. The second suction manifold and the
second discharge manifold are coupled to a second refrigeration
circuit separate from the first refrigeration circuit and operate
within a second temperature range different than the first
temperature range. A second controller is associated with the
second refrigeration unit to stage the second variable capacity
compressor and the second fixed capacity compressor based on a
comparison of a second operating condition of the second
refrigeration unit to a second refrigeration circuit set point.
[0014] A refrigeration unit for a refrigeration circuit in a
refrigeration system including multiple refrigeration circuits
includes a housing, at least one variable compressor disposed
within the housing, and at least one fixed compressor disposed
within the housing. A suction manifold is disposed within the
housing and is fluidly coupled to the at least one variable
compressor and to the at least one fixed compressor. A discharge
manifold is fluidly disposed within the housing and is coupled to
the at least one variable compressor and to the at least one fixed
compressor. A condenser unit is disposed within the housing, and a
controller is mounted to the housing and stages the at least one
variable capacity compressor and the at least one fixed capacity
compressor based on a comparison of an operating condition to a set
point.
[0015] A method includes selecting a first set point for a first
refrigeration circuit coupled to a first refrigeration unit having
a first variable capacity compressor and a first fixed capacity
compressor. The method also includes detecting a first operating
condition of the first refrigeration circuit, comparing the first
operating condition to the first set point, and staging the first
variable capacity compressor and the first fixed capacity
compressor based on the comparison. In addition, the method
includes selecting a second set point for a second refrigeration
circuit coupled to a second refrigeration unit having a second
variable capacity compressor and a second fixed capacity
compressor. The method further includes detecting a second
operating condition of the second refrigeration circuit, comparing
the second operating condition to the second set point, and staging
the second variable capacity compressor and the second fixed
capacity compressor based on the comparison.
[0016] Further areas of applicability of the present teachings will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
teachings, are intended for purposes of illustration only and are
not intended to limit the scope of the teachings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The present teachings will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0018] FIG. 1 is a schematic of a prior art refrigeration
system;
[0019] FIG. 2 is another schematic of a prior art refrigeration
system;
[0020] FIG. 3 is a schematic of a refrigeration system according to
the teachings;
[0021] FIG. 4 is another schematic of a refrigeration system
according to the teachings;
[0022] FIG. 5 is a block diagram of a controller according to the
teachings; and
[0023] FIG. 6 is a perspective view of a distributed refrigeration
unit according to the teachings.
DETAILED DESCRIPTION
[0024] The following description is merely exemplary in nature and
is in no way intended to limit the teachings, application, or
uses.
[0025] Referring to FIG. 3, a refrigeration system 110 according to
the teachings includes a plurality of distributed refrigeration
units 100A-D, each respectively piped to a discrete refrigeration
circuit 126A-D. Each distributed refrigeration unit 100 includes a
plurality of compressors 112, a condensing unit 120 and a
controller 132, collectively mounted to or on a housing of the
distributed refrigeration unit 100. The compressors 112 are piped
together with a common suction manifold 114 and a discharge header
116 to provide compressed refrigerant to the condensing unit 120,
where the refrigerant vapor is liquefied at high pressure. Piping
124 for each refrigeration circuit 126A-D delivers the high
pressure liquid refrigerant to a plurality of refrigeration cases
in a retail outlet floor space 108. The distributed refrigeration
units 100 may be disposed at an outdoor space 106, such as on a
rooftop or adjacent the building housing the retail outlet floor
space 108.
[0026] Each refrigeration case 122 is arranged in a discrete
refrigeration circuit 126 including a plurality of refrigeration
cases 122 operating within a similar temperature range and
connected by piping 124 to a respective distributed refrigeration
unit 100. FIG. 3 illustrates four circuits 126 labeled circuit
126A, circuit 126B, circuit 126C and circuit 126D. Each circuit 126
is shown to include four refrigeration cases 122, but those skilled
in the art will recognize that refrigeration system 110 may include
any number of circuits 126, and each circuit 126 may include any
number of refrigeration cases 122. Each circuit 126 will be
associated with its own refrigeration unit 100 and generally
operate within a temperature range dictated by the cooling demand.
For example, circuit 126A may be for frozen food, circuit 126B may
be for dairy, circuit 126C may be for meat, etc. Because the
temperature requirement is different for each circuit 126, each is
independently piped to a distributed refrigeration unit 100 via
piping 124. For example, circuit 126A is plumbed to distributed
refrigeration unit 100A; likewise for circuit 126B and distributed
refrigeration unit 100B, etc.
[0027] By distributing the capacity to deliver high-pressure liquid
refrigerant, and independently piping each circuit 126 to operate
within a certain temperature range, certain efficiencies are gained
and expenses avoided. For example, unlike a conventional
refrigeration system 10, there is no need for a pressure regulator
28 to control the evaporator pressure and, hence, the temperature
of the refrigerated space in the refrigeration cases 22. Further,
due to the distributed arrangement of the refrigeration units 100,
the condensing units 120 and controllers 132 are installed
integrally with the compressors 112 in the distributed
refrigeration unit 100, thereby ensuring piping and wiring to
factory specifications.
[0028] The distributed arrangement of a single refrigeration
circuit 126 per distributed refrigeration unit 100 provides the
efficiencies of parallel compressor operation that the central
plant architecture provides, but does so with significantly reduced
piping and refrigerant requirements. The distributed arrangement
also reduces the initial construction costs to the building owner,
as well as shortened construction due to the simplified
arrangement. Over the life of the system, it reduces energy
consumption and refrigeration quantity.
[0029] As illustrated in FIG. 4, by distributing compressor
capacity via the distributed refrigeration units 100, shorter runs
of piping and wiring are required as the distributed refrigeration
units 100 are disposed outside the retail outlet, such as on the
retail outlet roof or along an outside wall, at a convenient
location near where the refrigeration circuits 126 are disposed
within the retail outlet. Further, a distributed arrangement of
multiple smaller refrigeration units 100 saves cost over the
central plant approach, which often requires a large central
penthouse weighing upwards of 40,000 to 50,000 pounds and requiring
extensive steel structure to support the weight; or requires
significant space within the retail outlet and extensive field
piping to condensers mounted on raised steel platforms on the roof
of the retail outlet. By comparison, the distributed refrigeration
units 100 with integrated compressors 112, condenser 120 and
controllers 132, weigh approximately 1,000 to 3,000 pounds, which,
once optimally located, will not require additional structure and
typically require only increasing girder beam and joist size.
Further, the lighter weight allows the distributed refrigeration
units 100 to be transported as assembled at the manufacturing
facility. Compared to the total additional structural cost of
approximately $25,000 per unit for a penthouse for a central plant
approach, the additional structural cost of the distributed
approach is approximately $700 per unit.
[0030] The efficiencies gained by the distributed architecture
begin with the construction, which can be accomplished in a shorter
period of time as the condensers 120 are piped and wired at a
manufacturing facility and the distributed refrigeration units 100
are disposed proximate the refrigeration circuits 126 they serve.
This arrangement not only shortens installation time, but reduces
the labor costs associated with the piping installation. Further,
the cost of the piping (particularly as the cost of copper piping
has increased over recent years), hangers and insulation decreases
as less is required for the shorter runs between the distributed
refrigeration units 100 and the refrigeration circuits 126.
Further, because of the shorter runs, there is a lower refrigerant
requirement, helping retail outlet owners meet increasingly
stringent environmental protection standards. In terms of operating
efficiency, reduced suction line pressure loss and greater energy
efficiency is achieved as a direct result of the shorter pipe runs
and targeted operating temperature provided by the arrangement of
the distributed refrigeration unit 100 for each refrigeration
circuit 126.
[0031] As with a conventional system, high-pressure liquid
refrigerant is delivered to each refrigeration case 122 within its
respective refrigeration circuit 126. The refrigeration case 122
includes an evaporator (not shown) and expansion valve (not shown),
which may either be a mechanical or electronic valve for
controlling the superheat of the refrigerant. Refrigerant is
delivered by piping 124 to the evaporator in each refrigeration
case 122 where the refrigerant passes through the expansion valve,
and drops in pressure to change the high pressure liquid
refrigerant to a lower pressure combination of liquid and vapor. As
the warmer air from the refrigeration case 122 moves across the
evaporator coil, the low-pressure liquid returns to a gas, which is
delivered to the common suction manifold 114 for the compressors
112 within the distributed refrigeration unit 100. As before, the
compressors 112 compress the low pressure gas to a higher pressure
and deliver the high-pressure gas to the condenser 120, which again
creates a high-pressure liquid to begin the refrigeration cycle
again.
[0032] The controller 132 of the distributed refrigeration unit 100
may include an input/output board 134, a microprocessor 136, memory
138, and a communication port 140, as best shown in FIG. 5. The
controller 132 may be mounted on the outer housing of the
distributed refrigeration unit 100, as best shown in FIG. 6. The
controller 132 controls the compressors 112 through the
input/output board 134, which includes relay switches to turn the
compressors 112 on and off to provide the desired suction pressure,
as well as control one or more fans of the condensing unit 120 by
turning fan motors off and on, varying fan speed and/or using an
inverter on the fan motor. The controller 132 communicates through
communication bus 134 via the communication port 140.
[0033] The refrigeration system 110 further includes a
refrigeration controller 130, which is in communication with the
controllers 132 of the various distributed refrigeration units 100.
The refrigeration controller 130 may be an Einstein area controller
offered by CPC, Inc., of Atlanta, Ga., or any other type of
controller that may be programmed.
[0034] In one variation of the teachings, the controllers 132 may
include operating algorithms stored in memory 138 for compressor
capacity and condenser fan control, which programs are executed by
the processor 136. The controller 132 then communicates operating
status and measured parameter data to the main refrigeration
controller 130 via communication port 140, which may be connected
to communication bus 134. Such communication is typically wired,
but may more efficiently be accomplished using a wireless
communication protocol.
[0035] In another variation, the refrigeration controller 130
stores algorithms for compressor capacity and condenser fan
control, and a processor in the main refrigeration controller 30
executes the programs and communicates control signals to the
controller 132 for each distributed refrigeration unit 100. Again,
the communication between the main refrigeration controller 130 and
the controller 132 for each distributed refrigeration unit 100 may
be accomplished over communication bus 134 or through wireless
communication protocol.
[0036] For wireless communication, each controller 132 may include
a transceiver 142 (as shown in FIG. 5) for transmitting and
receiving wireless signals. The main refrigeration controller 130
similarly may include a transceiver 144 for transmitting and
receiving signals. Each transceiver 142, 144 may include a
transmitter and receiver capable of receiving and sending radio
frequency (RF) parametric data. Further, each transceiver 142, 144
may include a signal conditioning circuit. The transceiver may be a
stand-alone device positioned independently of the controller 132
or refrigeration controller 130. Further, the refrigeration system
110, depending on distance and the communication environment, may
require one or more RF repeaters 146 to overcome a limited
transmission range. In this case, each repeater 146 acts as a
bridge between the transceiver 142 of the controller 132 and the
transceiver 144 of the main refrigeration controller 130.
[0037] The controller 122 controls distributed refrigeration unit
100 based on set points established within the refrigeration
controller 130. Because the controller 132 is configured with a RAM
chip, microprocessor, and flash memory, it performs all control
functions even when communication to the refrigeration controller
130 is lost. Furthermore, this same configuration allows the
controller 132 to download the most recent control set points to
the refrigeration controller 130 after communication is
re-established. Similar to the refrigeration controller 130, the
controller 132 has various memory chips that are pre-programmed
with default set points. The controller 132 is capable of operating
the associated distributed refrigeration unit 100 as soon as the
controller 132 has been wired to the distributed refrigeration unit
100 and is receiving input data. Set points may also be altered at
any time from a hand-held terminal and are valid until a connection
between the controller 132 and the refrigeration controller 130 is
made. The controller 132 monitors input data from sensors connected
directly to it, and receives additional input data routed to the
refrigeration controller 130 from sensors connected to other
controllers or input boards.
[0038] Each distributed refrigeration unit 100 includes one or more
compressors 112 depending on the required capacity for the
refrigeration circuit 126 to which it is piped. Further, each
distributed refrigeration unit 100 may include at least one
variable capacity compressor 112'. Thus, if the distributed
refrigeration unit 100 includes a single compressor 112, it may be
a variable capacity compressor 112'. Where the distributed
refrigeration unit 100 includes two, three, four or more
compressors 112, at least one of the compressors 112 may be a
variable capacity compressor 112', but as many as two or all of the
compressors 112 may be variable capacity compressors 112'.
[0039] Variable capacity compressors 112', such as that disclosed
in U.S. Pat. Nos. 4,563,324; 6,120,255; 6,213,731; and 6,821,092,
each of which is expressly incorporated herein by reference, allow
efficient and accurate matching of compressor output to required
circuit capacity. Variable capacity compressors modulate compressor
capacity by one or more stepped amounts or infinitely to more
efficiently match capacity to load by allowing the compressor to
operate at full capacity and one or more reduced capacity modes.
Variable capacity compressors include variable speed compressors
and compressors having capacity modulation, such as by venting the
compression chamber and/or blocking suction.
[0040] The controller 132 uses a pressure measurement from a
transducer 150 on the suction side of the compressor 112 to compare
to a user defined set point. Through a PID comparison of the
pressure measurement and the set point, the controller 132 selects
compressor staging. The PID output is a capacity percentage needed
to achieve the set point.
[0041] In order to determine staging based on the percentage
capacity required, the controller 132 may employ a capacity control
algorithm or a data look-up table. The data look-up table includes,
for any given capacity, all possible combinations of compressor
staging. Based on a user-selected preference, the controller 132
under either scenario selects a staging for the capacity needed, or
moves a predetermined capacity towards the capacity requested so as
to minimize cycling of the compressors.
[0042] Once the new compressor capacity is selected there are many
compressor combinations for satisfying requested capacity. In order
to select a capacity, a controller uses the following criteria: (1)
minimizing cycling among the compressors; (2) equalizing run time
among the compressors; and (3) matching compressor on and off time.
The user may select whether equalizing run time or matching on and
off time is used in selecting a compressor combination for staging
a particular capacity. At a minimum, compressor staging for a given
capacity is decided based on minimizing compressor cycling.
[0043] Where a variable capacity compressor 112' is included in the
suction group, varying the capacity of that compressor 112' may be
by default the first option for achieving a given capacity. There
are limits, however, because it is not desirable to ramp up the
capacity of the compressor too quickly. Thus, within a given time
frame, the capacity of variable capacity compressor 112' may only
change by a user-defined amount. Thus, once this maximum is
reached, the controller 132 may use the capacity control algorithm
or data look-up table to complete staging for that given capacity.
Also, the capacity of variable capacity compressor 112' may be
limited to within a range where that compressor operates most
efficiently. For example, limiting the capacity of the variable
capacity compressor 112' to between fifty and eighty-five percent
of its maximum speed may be desirable. Thus, the controller 132
operates the variable capacity compressor 112' within this range
and uses the capacity control algorithm or data look-up table to
complete compressor staging for the necessary capacity. In this
scenario, the variable capacity compressor 112' cycles within its
range to meet small capacity changes.
[0044] A pressure control algorithm may be used to control suction
pressure input against the suction pressure set point. The result
of this control affects compressor outputs, which stage on and off
depending on outputs from the PID control. There are two main
control strategies for compressor control: (1) normal control; and
(2) fixed steps control.
[0045] Normal control enables the compressor control algorithm to
find the best possible combination of compressors within the
suction group and also satisfy any run time and horsepower
requirements. The desired percentage attained from the capacity PID
algorithm, referred to as a desired percentage, is used to
determine the next best combination of compressors. The desired
percentage is converted to desired horsepower by multiplying by the
total horsepower in the suction group. The process to find the
proper combination involves two different algorithms. One algorithm
finds combinations for suction groups that have variable capacity
compressors and the other for suction groups having only fixed
capacity compressors.
[0046] When using the data look-up table, two tables are built
representing all the possible permutations of compressors 112 and
the associated total horsepower for the suction group. Both tables
are then sorted from lowest horsepower combination to highest. A
capacity find algorithm searches for the combination that matches
closest to the desired horsepower, or desired percentage. When the
closest match is found, this new combination of compressors 112 is
stored and fed into a delay control algorithm. The delay amount is
calculated by comparing the new combination to the current
combination, and determining whether a compressor 112 or an
unloader is to be staged on or off, then picking the largest delay
amount amongst the set points. Once the delay is started, the
newest combination is stored and the current combination is used
until the delay time expires. During the time that the new
combination is stored, however, other combinations might be found
and saved over the previously-stored one. If a newer combination
has a calculated delay amount that is less than the current delay,
and the timer has already passed this delay amount, the delay is
cancelled and the newer combination is used at the outputs. By
using this method, the combination at the outputs always gets the
correct amount of delay. Variable capacity compressors 112',
however, are not included in calculating delays.
[0047] Because variable capacity compressors 112' may be controlled
to provide only a percentage of their horsepower, they can be used
to fine tune capacity when combined with fixed compressors to find
the closest match for the desired percentage. Fixed compressors
112, however, are treated as digital switches. When the compressor
112 is staged on, the output is set to high. With this simple
control, as the desired horsepower increases, more compressors 112
in the group are staged on to compensate for the need. A search
method is executed to look for a combination within the combination
tables. When the closest match is found, the new combination is
stored and fed into the delay control algorithm, as explained
above.
[0048] The fixed steps control strategy gives the user the
capability to provide its own combinations for the suction group.
For a maximum number of thirty steps, the user can determine what
stages should be on or off at every step. A desired percentage is
used as the input for determining the next step. Therefore, as the
percentage increases, the algorithm will increment to the next step
that matches the percentage. The next step value, which represents
a combination of stages, is then sent to the delay control
algorithm. If the percentage is decreasing, the algorithm will
decrement to the previous step. When the current step reaches the
first step or the very last step, the algorithm holds until the
percentage changes in the opposite direction.
[0049] The controller 132 controls fan speed for condensing unit
120 for scheduling, logging, and monitoring. The controller 132
supports three basic cooling strategies: (1) air cooling; (2)
evaporation; and (3) temperature difference. For each of these
strategies, the controller 132 uses PID control to a user-defined
set point to control operation of the fan by turning fan motors off
and on, varying fan speed, and/or using an inverter on the fan
motor.
[0050] For air cooling, multiple fans 160 may be used, in which
case they are sequenced based on the cooling required. The sequence
can be controlled to equalize run time among the several fans 160.
The amount of cooling necessary is determined by comparing the
pressure on the discharge side (as measured by transducer 152) of
the compressor and the user-defined set point. If a variable speed
fan 160' is used, the controller 132 sets the speed of the fan 160'
based on the same comparison. If a two-speed fan 160" is used, the
controller 132 selects the speed based on the cooling required, as
derived from the same comparison.
[0051] For evaporative cooling of the condensing unit 120, the
controller 132 operates a water valve (not shown) based on the
required cooling of a condensing unit 120. Further, the controller
132 operates a fan 160 for evaporation of the cooling water over
the condenser coils, and may be further fitted with a damper (no
shown), whose opening is varied by the controller 132. Again, to
determine the amount of cooling required, a compressor discharge
pressure measurement from transducer 152 is compared to a
user-defined set point.
[0052] For the temperature difference strategy for condensing unit
120, the controller 132 takes the difference between an ambient
temperature measurement from ambient temperature sensor 154 and a
discharge pressure measurement from transducer 152. The difference
is converted to temperature. While the temperatures being compared
are different for this approach, cooling is typically air-cooling
but could alternatively be evaporative.
[0053] With reference to FIG. 6, the distributed refrigeration unit
100 includes a housing lens 170 divided into a condensing unit
cabinet 172, a compressor cabinet 174, and an electronic cabinet
176. The condensing unit cabinet 172 houses the condensing unit 120
and condenser fans 160. The compressor cabinet 174 houses one or
more compressors 112, 112', as well as the section header 114 and
discharge header 116. The electronic cabinet 176 encloses the
controller 132 in an enclosure accessible from the exterior of the
housing 170. At least one of the compressors 112 may be a variable
compressor 112'. Further, while a pair of condenser fans 160 are
shown, one or more condenser fans 160 may be provided, and
condenser fans 160 may be variable speed condenser fans 160' or
two-speed condenser fans 160".
[0054] The description of the teachings is merely exemplary in
nature and, thus, variations that do not depart from the gist of
the teachings are intended to be within the scope of the teachings.
Such variations are not to be regarded as a departure from the
spirit and scope of the teachings.
* * * * *